The debate about whether there's something wrong with buying sex, and whether it should be illegal, is heated and unresolved. Amid the debate, however, one question is rarely asked - what motivates men to pay women to sleep with them?

"We first met online on a message board," says Fred, who is retired, "and I asked her if she would like to spend the night in a hotel with me."

He says it was like a first date, "getting to know each other, sounding each other out."

"Now we know each other so well that Fred just transfers the money to my bank online before I come to meet him," says Laura.

Fred lives in a remote rural area and for many years he was a full-time carer, looking after his mother. He says he didn't have a chance to meet people - so decided to pay for sex.

"It really wasn't so much the sex as wanting female company and if you are not getting out and socialising then it is very difficult to think about how you're going to get that."

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Some are motivated by a desire for female companionship as much as the sex itself

I wanted to hang on to my marriage... so the obvious thing was to pay for itRobert

"I ended up a highly sexed man married to a woman who really didn't enjoy sex - [or even] hugging, kissing and so on.

"She's an excellent, excellent partner. In every other way we got on like a house on fire, but just not in bed."

Robert squirrels away as much money as he can to buy sex.

"I wanted to hang on to my marriage," he says, "I wanted to do right as much as I could by my wife, so the obvious thing was to pay for it."

The ethical maze of prostitution

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The issue of prostitution is still a heated and unresolved debate in the UK

The idea that human beings could be for sale is ethically controversial. Yet sex workers often say they don't sell their bodies but, like other workers, simply put a price on their talents and skills. They argue that, if sex work was decriminalised and destigmatised, the associated problems would mostly disappear. Is there anything wrong with selling sex?

While Robert sees paying for sex as a way to preserve his marriage, Graham, in his 30s, thought it might be a way to avoid the complexity of relationships altogether.

For the first 30 years of his life, former civil servant Graham thought he would never be the sort of man who would pay for sex. But one weekend in Amsterdam he found himself walking the streets of the red light district with some men he had just met.

A girl beckoned them, but two of the men dismissed her. "We can get a better one," they said.

She turned to Graham. "You'll come upstairs with me won't you?" she said.

"At that time," Graham says, "I probably just couldn't see any barriers as to why I wouldn't."

He followed her to a red-lit booth and spent half an hour with her, chatting and having sex.

"It was amazing. It felt really romantic, it felt like we were condensing a relationship into just a couple of minutes."

Reflecting on his previous relationships and painful breakups, he wondered: "Maybe you don't need to do any of that. Maybe you can pay and have these just incredible moments of spontaneous, all over in half an hour… just… magic."

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The red light district in Amsterdam is Europe's most famous location for legal prostitution

Simon, a shy man, has never found meeting women easy. At 29 he decided to lose his virginity by paying for sex. But he was never comfortable with his decision.

"I've read stuff on the internet that it's not good emotionally for women," Simon, who is in his 30s, says. But it hasn't stopped him regularly visiting the same woman over the last few years.

"I've got a high sex drive and it is not just that I enjoy sex, but if I don't have sex after a while, I feel terrible physically."

If I don't have sex after a while, I feel terrible physicallySimon

Simon prefers to see the same woman because he is more relaxed with her than he would be with someone new.

But although he knows her quite well, he says he is under no illusions.

"If I wasn't paying her, she wouldn't dream of having sex with me."

Simon has had a couple of girlfriends in the last few years and while in those relationships, he says he stopped paying for sex. He hopes to be in another relationship again one day.

"I just prefer that the woman I'm having sex with wants to do it, not for money, but wants to be with me."